This invention relates to a pneumatic servomotor for an assisted braking.
More particularly, the present invention relates to a pneumatic servomotor for an assisted braking, of the type comprising a rigid axial casing, in which a substantially truncated-cone shaped transverse skirt is movable and integral with a piston for the actuation of an associated master cylinder, while it defines two pressure chambers inside the casing; of the type in which a substantially annular sealing diaphragm made of an elastomeric material is interposed between the casing and an outer peripheral area of the skirt; and of the type in which a substantially annular seal made of an elastomeric material is interposed between an inner area of the skirt and the piston.
Numerous implementations of servomotors of said type are well known.
According to a first known design, servomotors were provided, in which bearing faces of the sealing diaphragm and/or of the seal were accommodated inside a groove in the piston. Yet such design has the disadvantage of requiring a careful fitting of the bearing faces in question into the associated grooves, failing which some lack of tightness may occur between the skirt and the seal or between the skirt and the diaphragm, thus connecting the front chamber with the rear chamber of the servomotor.
In order to cope with such a drawback, a second design has been suggested, according to which a diaphragm is made in one piece with the seal and conforms to the rear face of the skirt.
The latter design theoretically eliminates any possible lacks of tightness, likely to appear between the skirt and the seal or between the skirt and the diaphragm, yet no particular arrangements are made for the elastomeric material to adhere to the skirt in a reliable manner. Should such material happen to separate from the skirt, then it might become slack and impair the tightness between the seal and the skirt, or the tightness between the diaphragm and the skirt.